1. Field of the Invention
The present invention relates to magnetic nanoparticles and methods of using magnetic nanoparticles for selectively removing biologics, small molecules, analytes, ions, or molecules of interest from liquids.
2. Description of the Related Art
Selenium is a trace element that is needed in small quantities for most human, animal and plant survival; however greater concentrations can have a detrimental effect on living species. Elevated concentrations of selenium have been and continue to be a major problem in regions of the western United States, other areas of the US, and all over the world.
Oxyanions of selenium have been identified as environmental toxins in drainage waters from irrigated agricultural soils that contain selenium. The environmental concern regarding selenium has been attributed to its potential to cause either toxicity or deficiency in humans, animals, and some plants within a very narrow concentration range. It has been observed that concentrations of selenate (Se042″) as low as 10 parts per billion in water can cause death and birth deformities in waterfowls. As a result, the United States Environmental Protection Agency (U.S. EPA) designated 0.01 mg/L Se as the primary drinking-water standard. Selenate is found in high concentration in areas of the western United States and irrigation activity can result in the movement of selenate to ground or surface waters
Irrigation and drainage from selenium rich soils leach selenium into the water of both groundwater and surface water. Aqueous selenium exists predominantly as selenate (Se042−) and selenite (Se032″). Of the two species, selenate is the more stable in aqueous solutions and thus relatively more difficult to remove. The concentration and the chemical forms of selenium in soils or in drainage waters are governed by various physiochemical factors including oxidation reduction status, pH, and sorbing surfaces.
Selenium can exist inter alia as selenide, elemental selenium, selenite, selenate, and selenium complexes with cyanite or organic bases. At present, physicochemical methods such as chemical precipitation, catalytic reduction, and ion-exchange are mainly utilized for removing Se from wastewater. Of these species, ion exchange favors selenocyanate over selenate and selenate over selenite, whereas the iron hydroxide adsorption has no affinity for selenocyanate and favors selenite over selenate. Since most refinery final effluents and natural waters include a mixture of selenate and selenite selenium species, it has been difficult to approach complete removal of selenium from refinery effluents or natural water using only one step. Furthermore, oxidation to, or reduction from, the selenate state is kinetically very slow which further inhibits optimization. Ion exchange also has not been a successful removal technique because selenate shows almost identical resin affinity as sulfate, which is usually present in a concentration of several orders of magnitude higher than selenate. Thus, the sulfate simply preferentially competes with selenium for resin sites. Furthermore, ion exchange resins become fouled when used to treat selenium wastewater and methods for regeneration are often inadequate and unpredictable.
It is known that microbial reduction of selenate (Se6+) into elemental selenium)(Se0) via selenite Satoshi Soda (Se4+) plays an important role in detoxification of soluble Se in the natural environment. Since elemental Se is of little or no toxicity and is easily removed from the aqueous phase due to its insoluble characteristics, this reductive process might be applied to develop wastewater treatment systems for detoxification and removal of soluble Se, especially selenate.
Current methods of water treatment are not highly effective for scale-up use, are energy intensive, and are associated with high cost. Previous attempted technologies for selenium remediation from water sources include biological processes (anaerobic-bacterial process, facultative-bacterial process, microalgal-bacterial process, and others), microbial volatilization, geochemical immobilization, heavy metal adsorption process, ferrous hydroxide process, membrane processes (reverse osmosis, forward osmosis), ion exchange columns, and other methods. Due to the lack of effectiveness few of the current technologies are implemented in the field, and large evaporation pools or land retirement has been the customary method of dealing with selenium problems in agricultural areas such as the San Joaquin Valley of CA.
Current methods of water treatment are energy intensive and use membrane technology or other complicated water treatment apparatuses. The present invention simplifies water treatment techniques and offers an efficient method of selenium remediation using less energy than other proposed technologies for water treatment while also limiting environmental impact from brine and other harmful bi-products. The present invention is cost effective and has a large positive environmental impact. This novel invention is an element, ion, or molecule specific, safe, repeatable, and cost effective means of selenium removal that is robust and uses minimal electricity as well as minimal environmental impact.
Desalination refers to any of several processes that remove salt and other minerals from water. Water is desalinated to convert it to potable fresh water. Most of the modern interest in desalination is focused on developing cost-effective ways of providing fresh water for human use in regions where the availability of fresh water is limited.
According to a Jan. 17, 2008, article in the Wall Street Journal world-wide, 13,080 desalination plants produce more than 12 billion gallons of water a day. Large-scale desalination typically uses extremely large amounts of energy as well as specialized, expensive infrastructure. A number of factors determine the capital and operating costs for desalination: capacity and type of facility, location, feed water, labor, energy, financing and concentrate disposal.
Moderately saline waters can be used for irrigation and agriculture purposes where strict standards that apply for drinking-water are not required. However, to-date, the energy required and the high cost of desalinating brackish waters and seawater have been the major constraints on large-scale production of freshwater from saline waters.
The energy & electricity requirements are estimated to be reduced by ˜70%, thereby making desalinated water more affordable for most crop irrigation. The cost estimation is based on the fact that the separation is conducted by applied magnetic field gradients from a permanent rare earth magnet, and hence does not require huge electricity consumption demanded by the high pressure feed pumps currently used in desalination processes to operate the process at 40-80 bars. The minimal energy costs involved for desalination using functionalized nanoparticles would be pumping feed water initially to the first stirred tank reactor and the energy required for continuous stirring in each tank.
Approximately 70% of the earth's surface is water covered, the vast majority of which is ocean and is unusable without desalination. Freshwater accounts for less than 3% of the total water on the planet, but most of this is locked in the two polar icecaps. Therefore less than 1% of freshwater is readily accessible for human use. Rising demand for potable and irrigation water is of increasing socio-economic importance worldwide and requires the utilization of sea, brackish and saline bore water for fresh water supply. Increasingly, water scientists and engineers are questioning the viability of the current practice of meeting the water demands for all users according to increasingly stringent standards. High free energy of hydration of highly hydrophilic ions such as sodium, potassium, fluoride, and chloride makes the removal of such ions from aqueous solutions a very difficult separation process.
Membrane based reverse osmosis (RO) separation process has become the standard approach for desalinating water all over the world. The process of desalinating water through reverse osmosis has historically been both capital and energy intensive mainly because of the high pressure (40-80 bars) requirements for permeation of water through RO membranes. Thus, while RO has proven to be a reliable method for desalination of water, its high electricity demands is the major impediment for continuous adoption of the technology for desalinating water. Furthermore, the related significant production of green house gas, moderate recovery rates, as well as bio and colloidal fouling of the membranes are some of the concerns with membrane based separation technology.
An alternative to RO for desalination would be a technology that consumes relatively less energy without compromising the effectiveness of salt removal for a given application.
Membrane processes have developed very quickly, and most new facilities use reverse osmosis technology. Membrane systems typically use less energy than thermal distillation, which has led to a reduction in overall desalination costs over the past decade. Desalination remains energy intensive, however, and future costs will continue to depend on the price of both energy and desalination technology.
A Jan. 17, 2008 article in the Wall Street Journal states, “In November, Connecticut-based Poseidon Resources Corp. won a key regulatory approval to build a $300 million water-desalination plant in Carlsbad, north of San Diego. The facility would be the largest in the Western Hemisphere, producing 50 million gallons [190,000 m3] of drinking water a day, enough to supply about 100,000 homes . . . for $3.06 for 1,000 gallons.
Israel is now desalinating water at an operating cost of US$0.53 per cubic meter. Singapore is desalinating water for US$0.49 per cubic meter. According to an article in Forbes, a San Leandro, Calif. company called Energy Recovery Inc. has been desalinizing water for US$0.46 per cubic meter. “Hydro-Alchemy, Forbes, May 9, 2008.”
The unsatisfactory energy costs of existing technologies demonstrate the need for new technologies and have resulted in research into various new desalination technologies. In the past many novel desalination techniques have been researched with varying degrees of success. The U.S. Government is working to develop practical solar desalination.
Research efforts at the Lawrence Livermore National Laboratory indicate that nanotube membranes may prove to be effective for water filtration and may produce a viable water desalination process that would require substantially less energy than reverse osmosis. “Lawrence Livermore National Laboratory Public Affairs (2006-05-18). “Nanotube membranes offer possibility of cheaper desalination”. Press release, http://www.11nl.gov/pao/news/news_releases/2006/NR-06-05-06.html”
Siemens Water Technologies had reportedly developed a new technology that desalinizes one cubic meter of water while using only 1.5 kWh of energy, which, according to the report, is one half the energy that other processes use. “Team wins $4 m grant for breakthrough technology in seawater desalination, The Straits Times, Jun. 23, 2008.”
A relatively new process, the “Low Temperature Thermal Desalination” (LTTD) uses low pressures inside chambers created by vacuum pumps and the principle that water boils at low pressures, even at ambient temperature.
In another area of water purification, systems currently utilized as a step in the potable water production process in ultrafiltration membranes use polymer membranes with chemically formed microscopic pores that use pressure to drive the water through the filter.
Ion exchange systems use ion exchange resin- or zeolite packed columns to replace unwanted ions commonly to remove Ca2+ and Mg2+ ions and replacing them with benign (soap friendly) Na+ or K+ ions. Ion exchange resins also used to remove toxic ions such as nitrate, nitrite, lead, mercury, and arsenic.
Disinfection is currently accomplished both by filtering out harmful microbes and also by adding disinfectant chemicals
In the last step in purifying drinking water, water is disinfected to kill any pathogens which pass through the filters. Common pathogens include viruses, bacteria, such as Escherichia coli, Campylobacter and Shigella, and protozoans, including Giardia lamblia and other cryptosporidia.
In areas with naturally acidic waters the water may be capable of dissolving lead from any lead pipes that it is carried in. small quantities of phosphate ion are added and the pH is slightly increased. Both assist in greatly reducing lead ions by creating insoluble lead salts on the inner surfaces of the pipes.
Some groundwater sources contain radium. Typical sources include many groundwater sources north of the Illinois River in Illinois. Radium is commonly removed by ion exchange, or by water conditioning.
Although fluoride is added to water in many areas, some areas such as parts of Florida have excessive levels of natural fluoride in the source water. Excessive levels can be toxic or cause undesirable cosmetic effects such as staining of teeth. One method of reducing fluoride levels is through treatment with activated alumina.